There are currently various systems for attaching a transportation accessory such as a roof box, an automobile roof tent or a roof rack to a vehicle's roof bars.
To attach an accessory such as a roof box, there are fast and anti-theft systems such as patent FR2836432, accessible only from inside the roof box.
However, to access it the user is required to reach the device located high up on top of the vehicle and in addition inside the roof box, which is difficult in the case of large vehicles.
Furthermore, the system takes up room inside the roof box, making loading more difficult and it is not possible to use this system in the case of a tent roof, where the floor must be absolutely flat for sleeping on.
Finally, the system is limited in terms of the width of the bars on which it can be fixed, which currently can cause problems with very wide wing-shaped bars.
There are other systems, used mostly for fixing transverse bars onto longitudinal bars, such as EP0894672, but they are difficult to use in the case of roof boxes and roof racks on transversal bars since it is difficult to gain access between the vehicle's roof and the roof box or rack.
Moreover, these systems do not have a usage range capable of gripping both very thin and very wide bars.
Finally, these systems include a large number of parts, which has an impact on the manufacturing cost.
Another such system is described in patent WO 94/21490, which uses a wedge system for tightening in all positions.
In this known device, a screw in the channel axis of the bar (or rail) tightens two identical grips.
The outer side of the grip is angled at about 60° and has a hole for the hexagon screw.
A 60° wedge is threaded to hold the screw and acts in the system as a nut.
A compression spring between the grips allows the lock to be preloaded using a small amount of force, enabling the system to be moved by pressing the wedge.
This system has some drawbacks, such as the wedge effect which relies on the screw and the angle of the wedge: there is a contradiction between the clamping force of the grips and the locking force of the wedges.
Depending on the wedge angle, one of the two forces will increase and the other decrease, although both are equally important.
Moreover, if the screw breaks, there is no longer any fastening effect, which may endanger the security of the load. Finally, the screw is pulled by the thread which moves radially under the wedge effect and is already pulled by its head, in the bore of the other grip, thereby pulling the screw in two directions and exposing it to additional mechanical stress, which must be avoided (risk of it breaking).
There are also very traditional fixing systems using flanges (of various shapes), which are not easy to use since they involve the tightening of nuts (or bolts) where the load rests on the bar, usually between the vehicle roof and the load, which has poor access and little room for the movements required. In addition, since the height of the bars from the vehicle roof varies widely from one vehicle to another, it is not uncommon for screws to be too close to the vehicle roof or even touch it, rendering the system unusable. Finally, these systems are not anti-theft.